Polystyrene color stabilized with a trialkyl phenol and an alpha cyanoacrylate



United States Patent POLYSTYRENE COLOR STABILIZED WITH A TRE- ALKYLPHENOL AND AN ALPHA CYANO- ACRYLATE Leo Costello, South Bound Brook, andJerome L. Dunn, Somerville, N .J assignors to American Cyanamld Company,New York, NFL, a corporation of Maine No Drawing. Fiied Jan. 30, 1962,Ser. No. 169,953

8 Claims. (Cl. 260--45.85)

This invention relates to protecting polymeric styrene compositionsagainst development on aging of excess coloration, particularly thatproduced by exposure to incident ultraviolet light. More particularly,it is concerned with a unique protective method for such compositionswhich method consists in disseminating therethrough a small amount of aprotective composition consisting essentially of a selected minor amountof a suitable tri-alkyl phenol and a major amount of a suitablealkyl-fi-anilino-u-cyanoacrylate.

Of the many industrially-available polymeric materials, polystyrene, dueto its intrinsic structure, alone or in copolymers, has a markedtendency to exhibit yellow coloration which becomes increasinglyapparent on aging. It has proved to be one of the most difiicult toprotect adequately against excessive discoloration, particularly thatcaused by ultraviolet radiation.

The protective method of the present invention is particularly wellsuited for this purpose. Therefore, for purposes of this discussion,polystyrene will be taken as illustrative. Accordingly, the inventionstill further contemplates polystyrene products protected by theaddition of the protective-agent composition.

Still more specifically, the phenol derivatives used as protectiveagents in this invention may be represented by the type formula:

came 0 (C 3),

wherein R is an alkyl radical of from one to about four carbon atoms.These compounds are not new per se and have been previously known asantioxidants for oils, fats and rubber.

The substituted cyanoacrylate may be represented by the formula:

wherein R represents hydrogen or methyl and R represents an alkyl offrom one to four carbon atoms.

Polystyrene, a Well known homopolymer which may contain small quantitiesof lubricants and/or colorants, has been found useful in a wide varietyof applications. In many of them the development of excessive yellowdiscoloration is undesirable. Therefore, many attempts have been made toprotect polystyrene against this effect of exposure to radiation in theultraviolet range (hereinafter abbreviated as UV or UV-radiation).

Primarily, this has been attempted by incorporating therein smallamounts of various known UV-absorbing compounds. Such attempts have beenpartially successful over relatively short periods of exposure. However,upon continued exposure, yellowing nevertheless continues to 3,134,750Patented May 26, 1964 Fee measured by a spectrophotometer in thefollowing formula:

Wherein, T is the percent transmission of the unexposed sample at theindicated wavelength and T that of the exposed sample at the indicatedwavelengths.

Based thereon, the following test procedure was developed. To parts ofpolystyrene the amount of protective material to be tested is added on atwo-roll mill. One roll is maintained at 350 F., the other at 250 F. Themix is blended continuously over a ten-minute period by repeatedlypassing the mix through the nip of the rolls for 70 passes. Samples ofthe resultant blended mix are compression molded into a 0.050" x 2" x 2"chip. Y.I. readings are taken before and after each designated exposureperiod in the Fade-ometer and the Y.I. is calculated according to theabove-noted formula. This procedure is used in the following discussionand specific examples and in obtaining the Y.I. values noted in thefollowing discussion.

It is also necessary to establish a measure of successful protection. Ingeneral, when the Y.I. exceeds a value of some 15-20 units, theresulting polystyrene is too yellow. It is considered unsatisfactory formany applications. A good result, which it is a principal object of thepresent invention to attain, is to so protect the polystyrene thatmaximum exposure periods are required before the Y.I. readings reachthis range. Less protection than about 1000 hours to Y.l=15 is notgenerally satisfactory. Accordingly, in the test work discussed below,unless needed for comparison, testing was stopped in most cases when aY.I. of about 20 units was obtained.

As noted above, it has been attempted previously to obtain protection byincorporation of UV-absorbers. Some benefits were obtained, but ingeneral the protec tion was not as sufiiciently lasting as desired.Duration of protection can be extended somewhat by using larger amountsof the UV-absorber. However, this is not a generally satisfactorysolution to the problem for several reasons.

Such attempts soon encounter certain inherent limitations. For example,many known UV-absorbers produce per se an initial yellowing effect onbeing added to polystyrene. There is, therefore, a definite limit on theamount which can be added before further addition thereof olfsets anyadditional benefit of increased protection. Other known UV-absorbersseem to offer good protection during initial exposure. However, whenpresent in useful amounts they tend to break down and thereafterseemingly produce an accelerated rate of discoloration.

There still remained, then, a definite need for a method of so retardingthis effect that even after prolonged exposure such yellow discolorationis minimized. Previously, such a result was not obtainable to thedesired degree by addition of UV-absorbers.

A major object of this invention, therefore, is to meet this demand; toproduce a marked improvement in the retardation of yellow discolorationand production of the resultant protected composition. As noted above,this has been accomplished by the use of the particular antij) oxidantsin combination with the particular UV-absorbers of this invention, bothin correct amounts.

As shown in the copending application of one of us, Serial No. 161,258;filed December 21, 1961; a marked improvement in protection is obtainedby disseminating through the polystyrene some 0.01 to 1.2 weight percentof a compound of the Formula I above. These compounds, despite the factthey have no previous history as UV-absorbers and are unique inpolystyrene, produce an unexpectedly good degree of protection. Periodsof some 800900 hours to a Y.I. of about units are obtainable.Nevertheless, a further increase in protection, if obtainable, is stilldesired. As was also pointed out therein, and in the foregoingdiscussion, the attempted use of UV- absorbing compounds alone for thispurpose encounters definite limitations and the duration of protectionremains less than that desired.

Surprisingly, in the present invention it has been found that acombination of the compounds of Formula I (above), i.e., those of theabove-noted copending application, with the anilinocyanoacrylate ofFormula II above, has an unexpected synergistic effect on the durationof the protection. Results are obtainable which could not be obtainedwith either alone. In fact, the protection is far greater than could beexpected from the results obtainable when each is used by itself.

As was noted above, in the protective composition of the presentinvention, each of the components should be used in the correct amount.In general, the phenols of Formula I (above) may be used in amountsranging from about 0.01 to about 1.0 weight percent of the polystyrene.However, the better practice and the preferred range is from about 0.02to about 0.5 weight percent. The cyanoacrylate of Formula 11 (above) maybe used in amounts of from about 0.05 to about 1.0 weight percent of thepolystyrene. Again the preferred range is somewhat shorter, usually fromabout 0.1 to about 0.5 weight percent.

Within the noted broad ranges, if the minimum of each is used, thecyanoacrylatezphenol ratio will be 5:1 (a); if the maximum of each, 1:1([2). If the maximum cyanoacrylate and minimum phenol is used, the ratiowill be 50:1 (c). If the minimum acrylate and maximum phenol is taken,the ratio would be 1:10 (d). Thus, from these figures alone, it might beconcluded that this ratio could vary from as little as 1:10 to as highas 50:1. This, however, would be deceptive, the weight percentages ofthe preceding paragraph represent only the actual amounts which may bepresent.

Such a conclusion should not be made. The weight percentages given arethe limits for that factor alone. In addition to the use of amountswithin these limits, they should also be so selected as to maintain aproper ratio each to the other. This ratio is a further limitation inand of itself.

In general, it is better practice, as noted above, to employ a majoramount of the cyanoacrylate and a minor amount of the phenol. Therefore,ratio (d) above, i.e., 1:10, will not be encountered in practice. Norshould the excess be as high as in ratio (c) above, i.e., 50: 1.

In general, the ratio usually will be found to have as a practical upperlimit about ratio (a) above, i.e., 5:1, although it may be increasedsomewhat, if so desired. As a lower limit, it will be found that itshould be about ratio ([1) above, i.e., about 1:1. Moreover, in practiceit will be found in most cases that this ratio range may be shortened tofrom about 3.5:1 to about 1.2: 1.

It will be found in many, if not most, cases that an average ratio ofabout 2.5 :1 will constitute good practice and is usually preferable.For that reason it has been used in further discussing this invention inconjunction with the following illustrative examples. Therein, unlessotherwise noted, all parts and percentages are by weight andtemperatures are in degrees centigrade.

&

Because of their quite long chemical names, a number of the compoundsused in the following examples are designated by symbols to simplifyreference thereto. These numbers designate the compounds shown in thefollowing listing:

Compound No. Chemical Name S-di-t-butyl-p-eresol.

4, G-tri-t-butyl phenol. 6-di-t-butyl-4-ethyl phenol.6-gi-t-butyl-4-i-propyl phenol. 0- it-butyl--n-propyl phenol. hylB-(N-methylanilino)-a-cyanoacrylate. methylfl-(N-methylanilino)-a-cyanoaerylate. isopropylfi-(N-methylanilino)-a-eyanoucrylate. t-butylfl-(N-methylanilino)-a-cyanoaerylate. ethyl B-anilino-a-cyanoacrylate.

n-butyl B-anilino-a-cyanoacrylatc.

The same identification symbol refers to the same compound wherever itoccurs in the following examples and discussion.

EXAMPLE 1 To illustrate the beneficial eifect of the substituted phenolsof the above-noted copending application of one of the presentinventors, 0.1 part of the illustrative compound is mixed with partsamples of commercial polystyrene and the Y.I. values determined. Thetest procedure outlined above is used. Illustrative average results areshown in the following table.

Similar results are obtained substituting A-3, A4 and A-5 as the testcompound.

EXAMPLE 2 In order to demonstrate the elfect of using only acyanoacryiate compound of Formula 11 (above), Example 1 is repeated,substituting 0.25 part of 13-1 for the 0.1 part per 100 of A-l. A Y.I.of 15 is reached in about 630 hours.

EXAMPLE 3 Example 2 is reieated substituting 0.25 part of 13-2 for theB-1 of that example. Illustrative results are shown in the followingtable.

Table II Y.I. after Exposure (in hours) Protective CompoundApproximately the same protection is obtained as with 13-1.Substantially equivalent results are obtained in repeating the examplewith 13-3, B4, B5 and B6. As the alkyl of R in Formula II (supra)increases from about two to about four carbons, the rate of retardingthe yellowing falls olf somewhat. Compounds in which R contains two ormore carbon atoms and R over four do not appear to be desirable.Compounds such as B-5 and B6 in which R is hydrogen producesubstantially the same protection, being only slightly inferior to thosewherein R is methyl. Accordingly, the preferred compounds are those inwhich R is methyl and R is methyl, ethyl, propyl or butyl as usedillustratively in the following examples.

EXAMPLE 4 Example 1 is repeated, replacing the phenols with a premixedprotective composition consisting essentially of A-2 and B1 in weightratio of about 1:25. The composition is used in amount of about 0.35part per 100 parts of polystyrene. Although a Y.I. of about 15 isreached in about 700 hours using A-1 alone and in about 630 hours withBl alone, using the combined composition after 1200 hours when the testis stopped, the Y.I. is still only about eight.

EXAMPLE 5 Example 4 is repeated substituting an equal weight of A-l forthe A-2. When the test is stopped after 1000 hours the Y.I. is stillsatisfactorily below 15. In repeating this experiment using A-3, A-4 andA-5 for A-1 and B2, B3, B4, B5 and B6 for Bl, substantially the sameresults are obtained.

In utilizing the present invention, it is feasible to add the twoprotective agents in succession on the mill or to add both separatelybut simultaneously. In general, however, less milling is required andgenerally better results are obtained if the two components of theprotective compositions are precombined in a uniform mixture as inExample 4 above. Moreover, this gives a larger Weight to be handled andis helpful in increasing the accuracy of measurement.

When using a precombined composition as the protective agent, itscomponents should be within the ratio ranges indicated above and itshould be used in such amount that both components are present withinthe indicated weight limitations.

We claim:

1. A polystyrene composition protected from developing excessive yellowcoloration on extended exposure to incident ultraviolet radiationconsisting essentially of homopolystyrene having dispersed substantiallyuniformly therethrough a sufiicient amount of a protective compositioncomprising a first compound of the formula s h I a)l wherein R is analkyl of from one to four carbons; and a second compound of the formulaR COOR:

wherein R represents a member of the group consisting of hydrogen andmethyl, and R represents an alkyl of from one to four carbon atoms; saidfirst and second compounds being present in amount sufiicient to providefrom about 0.01 to about 1.0 part of said first compound and from about0.05 to about 1.0 part of said second compound.

2. A composition according to claim 1 further characterized in that saidfirst and second compounds are present in a Weight ratio of from about1:1 to about 1:5.

3. A composition according to claim 1 further characterized in that saidfirst and second compounds are present respectively in from 0.02-05 and0.1-0.5 part per parts of polystyrene.

4. A composition according to claim 1 further characterized in that saidfirst compound is tri-t-butyl phenol and said second compound is ethylB- (N-rnethylanilino)- a-cyanoacrylate.

5. A composition according to claim 1 further characterized in that saidfirst compound is tri-t-butyl phenol and said second compound is methyl,8-(N-methylanilino)acyanoacrylate.

6. A composition according to claim 1 further characterized in that saidfirst compound is tri-t-butyl phenol and said second compound is ethyl[3-anilino-a-cyanoacrylate.

7. A composition according to claim 1 further characterized in that saidfirst compound is di-t-butyl-p-cresol and said second compound is ethyl[3-(N-methylanilino)- a-cyanoacrylate.

8. A composition according to claim 1 further characterized in that saidfirst compound is di-t-butyl-p-cresol and said second compound is methyl5- (N-methylanjlino)- a-cyanoacrylate.

References Cited in the file of this patent UNITED STATES PATENTS

1. A POLYSTYRENE COMPOSITION PROTECTED FROM DEVELOPING EXCESSIVE YELLOWCOLORATION ON EXTENDED EXPOSURE TO INCIDENT ULTRAVIOLET RADIATIONCONSISTING ESSENTIALLY OF HOMOPOLYSTYRENE HAVING DISPERSED SUBSTANTIALLYUNIFORMLY THERETHROUGH A SUFFICIENT AMOUNT OF A PROTECTIVE COMPOSITIONCOMPRISING A FIRST COMPOUND OF THE FORMULA